New Murray Explorer & Ackermann correction

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MurrayMauler

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I picked up this Murray Explorer kart off CL for $200.



It had a solid 6.5hp stock Tecumseh that needed a new carb and the recoil assembly rebuilt with new cord. I also replaced the brake pads, fitted new tires all around and a new 30 series driver clutch and belt since the original was seized solid with rust. I initially ordered a seat cushion from BMI Karts, but it was too small and didn't cover the seat pan completely. We used old pillows while I found a seat, lol.



Decided to return it and hit up a local salvage yard for a cheap adjustable manual seat. Scored one at a local import salvage yard from a 2007 Kia Rio for $40! Welded in some mounting tabs and we were riding in style and comfort.



Once my daughter and I took it for a few rides, it became obvious is was very difficult to steer, especially at low speeds. I did some digging on this site (great resource of info) and found out our kart had basically no Ackermann built into the stock leading control arm steering setup.

To solve this I cut and welded a "T" from some 1.5"W x 3/16" flat bar I got at HD, and some new grade 8 hardware from TSC. Decided to put the offset holes at 1.5" apart, or 3/4" left and right of the original tie rod connection point.





The difference is really noticeable and the kart steers so much easier at low speed now (no front tire scrubbing). She's a hoot to drive, and already scheming about a Predator 420 and 40 series clutch set. My only concern is my daughter already drives it flat out on our street, and my phone's GPS already verified 34.8 MPH with the old Tecumseh!

 

gman3850

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a stock 420 with comet 40 will be slower in the top end than the 212/ tecumseh. This is do to the fiinal drive of the clutches. I believe the comet 30 is .90:1 overdrive while the comet 40 is at a 1:1. But it will have more power off the line
 

Melloreel

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Nice job. The seat really blows me away. I was going to rebuild the current seat, but now I want one like that! Did you replace the throttle cable, and if so what type? I'm having trouble finding one. Thanks.
 

mckutzy

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Get a universal brake cable for a bicycle, cut to length, from wallmart. About the easiest way out there...
 

Melloreel

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Melloreel, the throttle cable on ours is original. It has a return spring in-line on the cable, before the engine to assist.

Thank you. Can you post a pic of how the cable is attached to the frame? The welded bracket that the cable slides thru? Into? Before it attaches to the rod? My Manco uses a threaded cable, and I'm not sure what stops the cable from sliding thru.
 

MurrayMauler

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Yes, rod #59 slips through boss on the frame, then the small washers (#31) and spring (#46) and is retained by the cotter pins. This provides the return pressure on the gas pedal. Hope this helps.
 

bob58o

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a stock 420 with comet 40 will be slower in the top end than the 212/ tecumseh. This is do to the fiinal drive of the clutches. I believe the comet 30 is .90:1 overdrive while the comet 40 is at a 1:1. But it will have more power off the line

True, but if going to change the engine, why not change the gearing as well? I don't want people thinking you CAN'T go faster with a bigger engine, because you certainly CAN.

It will only be slower if you don't change the gearing.
A 420cc engine will have more torque than a solid 6.5 HP Tecumseh (not sure how a Tecumseh that needs a new carb and other work is solid, but hey :lolgoku:) .

Any way the added torque that comes the extra cc's means you can gear it for more top end and still maintain enough torque at the wheels on the low end.

For example:
8 ft lbs @ 7.0:1 gearing with a 2.7 : 1(30 series) = 151 ft lbs at axle
18 ft lbs @ 3.5:1 gearing with a 2.4 :1(40 series) = 151 ft lbs at axle

Both will have about 182 lbs of linear force ( 182 ideal, Realistically maybe 150 lbs) pushing the kart at TC engagement (assuming 20" tires) ...so you'd loose no bottom end.

BUT...

3600 engine RPM 7.0 :1 with 0.90 : 1(30 series) = 571 axle RPM
~34mph @ 3600 RPM (if 20" tires)
3600 engine RPM @ 3.5 :1 with 1.00: 1(40 series) = 1,029 axle RPM
~61mph @ 3600 RPM (if 20" tires)

So adding a bigger engine can give you more bottom end, if that's what you want...
OR
More top end if you gear for it.
Especially with Torque Converters. C Clutches are a little different.

If geared 3.5:1 with a Centrifugal Clutch that engages at 2000 RPM with 20" tires....
2000 engine RPM = 34mph. Probably going to burn up clutches pretty fast. Going to take a while to get up to 34mph with 20" Tires and 3.5:1 gear ratio.

A 40 series TC engaging at 2000 RPM with 3.5 :1 gear ratio (x2.4 : 1) = 14mph, plus it has the gearing advantage to get to 14 mph pretty fast.

Now I'm rambling.
Its just been a while since i did a math problem example on here.:roflol:
 

mckutzy

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GAB..... There's an expression I haven't heard in a long while...

Interesting breakdown Bob, thanks....
 
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